1. Field of the Invention
The invention relates to a power converter. More specifically, the invention relates to a power converter having the function of detecting an insulation resistance, and further relates to a vehicle equipped with the power converter.
2. Description of the Related Art
To ensure safety from electrification, the ISO (International Standards Organization) standard and the ECE (Economic Commission for Europe) standard require that a certain insulation resistance value be ensured for a certain voltage. Namely, in a system with an insulation resistance rate KR (Ω/V) prescribed as a standard value and with an operating voltage Vs, it is necessary to ensure an insulation resistance R=KR×Vs (Ω).
Accordingly, it is important, from the standpoint of safety, to precisely detect an insulation resistance during operation, and Japanese Patent Application Laid-Open No. 2002-325302 discloses an electric leakage detector that precisely detects electric leakage of a power unit that drives a motor for causing an electrically driven vehicle such as a hybrid car, an electric vehicle or the like to run.
Further, in a system composed of an electric load and a power converter (power unit) that generates a power for driving the electric load, there is also known a construction wherein the power converter has not only the function of performing power conversion between direct current and alternating current, but also the function of converting the voltage level. For instance, Japanese Patent Application Laid-Open No. 2003-134606 discloses a hybrid vehicle driving unit having a construction wherein an input voltage is boosted by a voltage-boosting converter and then converted into an alternating voltage for driving a motor unit.
However, neither Japanese Patent Application Laid-Open No. 2002-325302 nor Japanese Patent Application Laid-Open No. 2003-134606 discloses a construction wherein the operating condition of the power converter (power unit) is varied at the time of degradation of the insulation resistance. Thus, if the insulation resistance has degraded, there is no alternative but to stop operation of the converter (unit) to ensure safety or to continue to operate the converter (unit) under the same condition that does not take account of improvements in safety.